1. Field of the Invention
The present invention relates to apparatus and methods for removal of heat from electronic devices. In particular, the present invention relates to a vapor chamber in conjunction with a heat sink for the removal of heat from a microelectronic die.
2. State of the Art
Higher performance, lower cost, increased miniaturization of integrated circuit components, and greater packaging density of integrated circuits are ongoing goals of the computer industry. As these goals are achieved, microelectronic dice become smaller. Accordingly, the density of power consumption of the integrated circuit components in the microelectronic die has increased, which, in turn, increases the average junction temperature of the microelectronic die. If the temperature of the microelectronic die becomes too high, the integrated circuits of the microelectronic die may be damaged or destroyed.
Various apparatus and techniques have been used and are presently being used for removing heat from microelectronic dice. One such heat dissipation technique involves the attachment of a high surface area heat sink to a microelectronic die. FIG. 5 illustrates an assembly 200 comprising a microelectronic die 202 (illustrated as a flip chip) physically and electrically attached to a substrate carrier 204 by a plurality of solder balls 206. A heat sink 208 is attached to a back surface 212 of the microelectronic die 202 by a thermally conductive adhesive 214. The heat sink 208 is usually constructed from a thermally conductive material, such as copper, copper alloys, aluminum, aluminum alloys, and the like. The heat generated by the microelectronic die 202 is drawn into the heat sink 208 (following the path of least thermal resistance) by conductive heat transfer.
High surface area heat sinks 208 are generally used because the rate at which heat is dissipated from a heat sink is substantially proportional to the surface area of the heat sink. The high surface area heat sink 208 usually includes a plurality of projections 216 extending substantially perpendicularly from the microelectronic die 202. It is, of course, understood that the projections 216 may include, but are not limited to, elongate planar fin-like structures and columnar/pillar structures. The high surface area of the projections 216 allows heat to be convectively dissipated from the projections 216 into the air surrounding the high surface area heat sink 208. A fan 218 may be incorporated into the assembly 200 to enhance the convective heat dissipation. However, although high surface area heat sinks are utilized in a variety of microelectronic applications, they have not been completely successful in removing heat from microelectronic dice which generate substantial amounts of heat. One issue which may contribute to this lack of success is the fact that the geometry of standard high surface area heat sinks results in an air stagnation zone over the center of the heat sink (generally where the most heat is being generated within the microelectronic die). This air stagnation may occur even with the use of the fan 218.
Another known method of removing heat from a microelectronic die is the use of a xe2x80x9cheat pipexe2x80x9d or xe2x80x9cvapor chamberxe2x80x9d 240, as shown in FIG. 6. A vapor chamber 240 is a simple device that can quickly transfer heat from one point to another without the need for external energy input. The vapor chamber 240 is generally formed by creating a low-pressure atmosphere within a sealed chamber 242 which contains a xe2x80x9cworking fluidxe2x80x9d 244, such as water or alcohol. The sealed chamber 242 is oriented with a first end 246 proximate a heat source 248. The working fluid 244, which is in a liquid phase proximate the heat source 248, increases in temperature and evaporates to form a gaseous phase of the working fluid 244, which moves (shown by arrows 252) toward a second end 254 of the sealed chamber 242. As the gaseous phase moves toward the sealed chamber second end 254, it condenses to again form the liquid phase of the working fluid 244, thereby releasing the heat absorbed during the evaporation of the liquid phase of the working fluid 244. The liquid phase returns to the sealed chamber first end 246 proximate the heat source 248, wherein the process is repeated. Thus, the vapor chamber 240 is able to rapidly transfer heat away from the heat source 248. Various configurations of heat pipes and high surface area finned heat sink have been used to cool microelectronic dice, but they have not been entirely successful in efficiently removing heat from microelectronic dice which generate substantial amounts of heat. One issue which may contribute to this lack of success is the fact that xe2x80x9chotspotsxe2x80x9d occur in specific locations within the microelectronic dice. The current configurations do not compensate with a higher heat removal for these hotspots. Thus, the circuitry at or proximate these hotspots can be thermally damaged.
Therefore, it would be advantageous to develop apparatus and techniques to effectively remove heat from microelectronic dice while compensating for thermal variations, such as hot spots, within the microelectronic dice.